Flow cytometry is the dominant method of counting red blood cells, white blood cells, and so forth. When a company is developing a flow cytometer, validation of the results from the machine is done by a human looking through a microscope and visually counting the cells on a sample smeared over a glass slide. Electric Cell-substrate Impedance Sensing (ECIS) determines how fast cells grow in a laboratory dish by measuring the impedance of the cells as they are growing. The cells block the electric field lines, and impedance increases as the cells grow and cover more and more of the sensor. Once the cells have completely covered the sensor, the impedance asymptotes.
The existing methods suffer from several limitations. For example, flow cytometer results take some time to obtain because blood samples are usually taken to a laboratory to be prepared and then run through the flow cytometer. Visual inspection to count cells is tedious for the human who has to do it and is of course prone to human error. Visual inspection results also take a considerable amount of time to obtain for the same reasons as the flow cytometer results. ECIS provides a single scalar measurement for the growth rate of a colony of cells on top of the sensor. No information is available as to how the cells cover the sensor, how many cells there are, concentration of cells, how the cells move as they grow, or the like.